1. Technical Field
The present invention relates to a piezo actuator and a lens actuating module using the piezo actuator.
2. Description of the Related Art
Generally, personal portable terminals such as electronic devices, mobile phones or PDAs have additional functions as well as a main function. Currently, many electronic devices additionally have a camera function to make them appeal to consumers. Thus, a market for camera modules mounted on the electronic devices has been gradually expanding.
In order to satisfy the demand of the market, the camera module has been developed to have additional functions including an auto-focusing function, an optical zoom function, and an Optical Image Stabilization (OIS) function, in addition to a fixed focus function.
Especially, in order to realize the additional functions of the camera module including the auto-focusing function, the optical zoom function, and the OIS function, a lens actuating module using an actuator for transferring a lens, for example, an actuator of a step motor type, a Voice Coil Motor (VCM) type, or a piezoelectric type is essentially required. In recent years, as the personal portable terminals require the composition of multiple functions and miniaturization, the camera module applied to the personal portable terminal mainly uses the piezoelectric type which is advantageous in terms of miniaturization and reliability.
A lens actuating module using piezoelectric elements is shown in FIGS. 1 and 2. FIG. 1 is a view illustrating the lens actuating module disclosed in U.S. Pat. No. 6,215,605. In the conventional lens actuating module, piezoelectric elements 11 and 12 are fixed to base blocks 21 and 22 and displacement is transmitted to driving rods 16 and 17, so that lenses L2 and L4 are transferred by preload generated from slide parts 31a and 32a, inertia force of lens holders 31 and 32, and acceleration effect. According to the waveform of voltage applied to the piezoelectric element 12, the lens holder moves along with the driving rod or slides so that it can retain its position, and thereby the lens is transferred. Further, the lens may be transferred in opposite directions.
When the lens actuating module of FIG. 1 is arranged in the configuration of FIG. 2, and the displacement of one of the piezoelectric elements 11a and 11b which are arranged to be adjacent to each other is transmitted through a base block 13, the displacement may be undesirably transmitted to another lens.
Thus, a groove 13g is formed in the base block 13 so as to prevent the transmission of displacement between piezoelectric elements. Such a groove complicates the structure, causes the lens actuating module to be difficult to manufacture, and cannot completely solve displacement interference between the piezoelectric elements.
Further, the length of each driving rod 16 or 17 which is moved forwards and backwards through the piezoelectric element 12 to transfer the lens is limited by the size of the piezoelectric element. The length restriction of the driving rods 16 and 17 limits the lens transfer length, so that it negatively affects the performance of a product.
Since the driving rods 16 and 17 are fixed, it is impossible to change the length of a barrel in which the lens is held. In addition to a space for the lens transfer length, an additional space for receiving driving elements is required, so that it is difficult to realize the miniaturization of an entire module. Further, only one end of the lens is supported by each driving rod 16 or 17, so that the lens has asymmetric displacement when the lens actuating module is driven, thus leading to unstable driving.